The present invention relates to a self-cleaning filtering apparatus for use in a material treating system of the type having a vessel in which material is subjected to treatment by fluid that is recirculated and conditioned for re-use, and more particularly the present invention relates to a self-cleaning filtering apparatus of this type in which the contaminant containing fluid from the self-cleaning function is itself filtered by discharge through a collector and back into the circulating fluid.
In many material treatment applications where material is subjected to treatment by a circulating flow of fluid that is recirculated and conditioned for re-use, the material being treated creates undesirable contaminants in the fluid being circulated, which necessitates the use of some kind of filter. However, in many such applications, the quantity of contaminant accumulating as a result of the filtering operation has the undesirable effect of clogging the system or significantly reducing the ability of the fluid to flow effectively through the application without close attention to and undesirable changing of the filter material during operation of the apparatus.
This problem of contaminant buildup in a recirculating treatment system is of particular concern in textile processing systems that inherently produce lint as a particulate contaminant in the recirculating treating fluid. For example, in piece dyeing machines the fluid is passed through the fabric or the fabric is passed through the liquid to effect dyeing and this inherently causes considerable agitation of the fabric. Further, it is common for the fabric to be continuously re-aligned to avoid recurring setting of folds that could cause creases or crush marks. For these reasons, piece dyeing systems commonly are provided with transport reels for moving the fabric by frictional contact and with jets or overflow boxes for moving the fabric and to create the fluid interchange with the fabric by velocity differences as the fabric travels through the system. The greater the difference in reel velocity and fabric velocity, or liquor velocity and fabric velocity, the greater will be the tendency for the fabric to shed lint.
Once in the circulating system, the lint will tend to clog the system, starting with the points of greatest restriction to flow. In many cases, these will be the jet orifices. As the area of the orifice is reduced by lint build-up, the velocity increases, thus increasing the tendency to shed lint. Simultaneously, the volume of liquor passing through the jet is reduced by the increased restriction, and the fabric tends to slow down, thus increasing the relative speed through the fluid and the fabric, and between the driven reel and the fabric, thereby increasing further the amount of lint given up by the fabric. The net result of all of this is a very drastic reduction in the dyeing efficiency of the system and a corresponding reduction in the quality of the goods being processed. With some fabrics it would be impossible to perform satisfactory dyeing without some means of removing the lint from the circulating fluid without prolonging the dyeing process to an economically prohibitive length.
The traditional attempt at solution to this problem has been to incorporate a filter into the circulating system. For example, filters have been used consisting of enlarged cylindrical sections in the recirculating system containing one or more perforated cylindrical filter elements at a selected location in the system, such as at the point of discharge from a circulating pump and prior to flow through the heat exchanger back into the vessel in which the dyeing takes place, thereby protecting the heat exchanger, valves, jets and other downstream components from the effect of lint in the circulating fluid.
Even with such filtering apparatus, piece dyeing systems require skill and diligent attention on the part of the operator because the vital and delicate balance between the traction provided by the jet and the traction provided by the reel is being continually upset at the filter accumulates lint and alters its resistence to fluid flow. As the dye cycle progresses it is not uncommon for the rate of flow of circulating fluid to be reduced to half of its original rate and in extreme cases for it to reduce to a mere trickle, and to render the machine, if not unusable, then uneconomical as all performance criteria, e.g. rate of temperature rise, rate of bath circulation, rate of cooling, rate of washing, are similarly reduced. At the same time, the undesirable effects of reel slippage on the fabric quality are taking place. Furthermore, even where the filters do not accumulate enough lint to affect pump performance, a small amount of lint remaining in the filter could result in color contamination if the next dyeing cycle will be performing a dyeing of a lighter shade.
A further significant problem is that of cleaning of the filters between cycles to remove the lint that has accumulated. In some instances textile fabric bags are used for the filter material, which may be thrown away and replaced by clean bags, but are otherwise susceptible to the same problems during operation as described above and are not as capable of handling the large flow of fluid as perforated sheet metal or wire mesh screens that suffer from the problem of cleaning between cycles. With perforated sheet metal or wire mesh screens, the lint tends to straddle the ridges between the holes, and the ends of the fibers of lint tend to knot on the opposite side. The appearance of a clogged screen is of a layer of felt on both sides, or of a thick mass of felt with the screen material buried in the center. Because of the turbulence from the flow of fluid the lint fibers are often firmly locked together. Cleaning the filter often involves vigorous scrubbing with a wire brush and may even require the material to be burned off with a blow-torch.
However, this locking and felting process is not instantaneous, and can be prevented entirely if the lint is removed as soon as it is trapped. It is, therefore, desirable that the lint should be removed from the circulating system on a continuous basis as it is produced during operation so that it is not permitted to cause the effects described above.
Self-cleaning filtering apparatus are known in the prior art in applications other than textile processing. For example, U.S. Pat. No. 3,994,810 discloses an onstream backflush filter in which a cylindrical filter element is continuously cleaned during operation by an annular head that reciprocates across the interior surface of the cylindrical filter element and has a peripheral opening and interior passage for flow of fluid containing the contaminant that is being cleaned from the interior surface of the cylindrical filter element to a discharge location, such as a drain, exteriorly of the apparatus. As the contaminant containing fluid being backflushed in the self-cleaning operation is discharged from the apparatus, this prior art type filter is not practical for use in a system in which the fluid is recycled and conditioned without undesirably having to periodically add fluid or components to the system to make up for that discharged in the backflushing.
In contrast, the present invention provides a self-cleaning filtering apparatus that can be effectively in a material treating system in which a treating fluid is recirculated and conditioned.